Questions about compasses

[hunter63]

I still have my Dad's WWII issue compass.

I do as well.....It worked good enough to get him out of China when his B-29 went down.......good enough for me.
Wasn't all fancy, just in a brass case...not sure if it's have radium on it or not.

[hunter63]

MF was a forest ranger....from the towers to office to, fire crews, hone lineman and a little game warden (deputing)...on the side.

Came home with the Smokey The Bear Costume when I was in about 1 or 2 grade....It was like finding out the Santa was your father.

The head smelled like tobacco, ....cigarettes and Copenhagen, sweat and BO........sorta like a real bear.......
I was heart broken to find out that he wasn't real.......

[crashdive123]

It probably had radioluminescent paint on it, but has long since lost its glow capabilities.

As a side note.....before the hazards of this material were known, the people that put the material on the watches and compasses (mostly women) used small artist brushes to accomplish that task. To keep a fine point on their brushes they would "twirl" them in their mouths. As can be expected, many came down with various forms of mouth and tongue cancer.

[hunter63]

There was a heck of a story about that in Mystery at the Museum....They even painted their teeth to go out on the town....

[Wise Old Owl]

My understanding may differ from the rest of the posts. Today the licensing and survey math is incredibly difficult and may have nothing to do with "professional" I am well aware that today's "plastic mass produced compass" is sold in countries that it is used for. In short you cannot transport a compass from the USA to Australia and expect it to be exact. Compasses are calibrated in a factory and checked by humans to be accurate for the country they are sold in... As for the old stuff... there is another rub.. In my lifetime the location of Valley Forge has changed declination from old maps of 12° to now close to 14° from true north over some 30 years. The real magnetic north pole is racing towards Siberia.

So lets put this on a plate. The "really good stuff works in every place on the earth for the time period issued." if a Marine issued compass with stuff that glows and will kill a nubie staring at it in the dark. It must be the right stuff. Thats my take - I am sticking to it...

[sjj]

In cold country, another consideration is cold weather performance.

[Rick]

Again, excellent points, sjj. Over the years a lot of different liquids have been used to dampen compass needles. Water, denatured alcohol and clear kerosene were all used. Sometime in the '60s it became the "standard" to use odorless mineral spirits. Today, that's what you'll find in most of the affordable compasses. The higher end compasses use a liquid called Isopar L. It, too, is a hydrocarbon made from petroleum. Obviously, all this depends on the manufacturer and the quality of the compass but for most of us mineral spirits is what dampens our compass needle. All of these liquids have to be degassed to avoid bubbles appearing in the compass. Nearly ever liquid has air suspended in it and degassing the liquid in a vacuum allows the fluid to be purged of air. It can then be used in a compass. If not degassed the air would eventually free itself and a bubble would form. As sjj correctly stated bubbles can still form from cold and elevation but those are bubbles formed when the mineral spirits (or whatever liquid) contracts. Warming the compass and/or returning to a lower elevation generally expands the liquid and the bubble "disappears".

Another note to consider. If you own one of those radio-luminescent compasses made up to the 1950s just remember they are highly radioactive even though they no longer glow in the dark. Most of those were painted with a mixture of radium and copper. Radium has a very long half life so even today if the compass leaks or breaks it will expose you to very dangerous levels of radium.

[sjj]

Thanks Rick - I learned something new. I'm also reminded of the time you explained to me how easy it is to re-magnetize a compass that has been compromised.

[Rick]

For those that are interested...we have so many magnets around us every day, I even have them in my glomitts to hold the finger end open, that it's easy for one to wind up next to a compass. When that happens, you can find your compass pointing south instead of north. You can re-magnetize your compass needle by using a strong magnet, preferably one in which you know the poles, and stroking the needle with the south pole of the magnet. Stroke in one direction only. If it doesn't work flip the magnet over and try again. If it still doesn't work find a stronger magnet.

[hunter63]

...........

Another note to consider. If you own one of those radio-luminescent compasses made up to the 1950s just remember they are highly radioactive even though they no longer glow in the dark. Most of those were painted with a mixture of radium and copper. Radium has a very long half life so even today if the compass leaks or breaks it will expose you to very dangerous levels of radium.

One of the American Scientific Club kits had a cloud chamber (plastic peanut butter jar)....some cardboard tunes, lens and filters....and a cork with a pin....painted with radium.....You could actually see different colored trails in the cloud...of radiation.
The was a warning on it at the time.....from the 1950's

[finallyME]

I was trained on compasses in the military with a lensatic. But, I ditched that when I bought my Brunton (silva ranger equivalent). I will always claim that a good baseplate compass with a sighting mirror is easier to use, lighter, easier to learn on, and easier to sight, than any lensatic. Plus, it has declination adjustment. This really becomes evident when I have to teach 12 year old boys how to use a compass. Trust me, a baseplate is much easier.

http://www.amazon.com/Suunto-SS00425...runton+compass

[Tokwan]

Boy, I'm really glad I joined this forum. Even though I am from another part of the world, in a place where the forest, climate, humidity, the language, customs are totally different, but what we use are almost identical. I too have a Silva Ranger and the Military compass. However, I always carry a Garmin 60 csx gps with some spare batteries and the Silva Compass as backup. It gives me a peace of mind.

[ninjasurvivor]

I can get buy with cheap compasses. The main thing is that they give me a consistent reading so I can keep a steady heading. Whether it is pointing me to "true" north or "magnetic" north, I don't really care. My goal is not to make it to the north pole to see Santa Claus. I just need a measure of what direction I am heading so I can take that into account on the way back.

[Rick]

Then you don't understand declination. It has nothing to do with reaching the North Pole and everything to do orienteering.

[crashdive123]

I can get buy with cheap compasses. The main thing is that they give me a consistent reading so I can keep a steady heading. Whether it is pointing me to "true" north or "magnetic" north, I don't really care. My goal is not to make it to the north pole to see Santa Claus. I just need a measure of what direction I am heading so I can take that into account on the way back.

I take it you don't use a map, but rather just head in a general direction?

[ninjasurvivor]

I take it you don't use a map, but rather just head in a general direction?

Correct. The fact of the matter is I don't typically go in areas which are foreign to me and require the use of maps and orienteering. I am familiar with how to do that, but I haven't as of yet needed to do that. Usually I have visible landmarks that would allow me to have a continual point of reference.

Recently I was in a vast woodland which I'd never been to. While hiking deep into the woods I kept checking my compass to make sure I stayed on a northwesterly heading. On the way back, it was a simple as heading southeast. My cheap Chinese compass got me where I needed to be. No map required. But I have to say that without the compass I may have gotten seriously sidetracked or lost.

[ElevenBravo]

Ive used the USGI Lensatic compass for 3 decades, and continue to do so.. I trust it.

They come in two flavors, one is NOT true USGI, its built the same but is illuminated by light gathering material. The REAL one uses radioactive glow dots just like your night sights... One is $30, the other is $130... Id urge you to go real deal.

EB

[tjwilhelm]

I may have posted this here before. If so, sorry.

Here's a video I made last year about magnetic declination, for whatever it may be worth:

[crashdive123]

Great vid and demonstration Tim.

[ninjasurvivor]

I'm not sure I fully understand lensatic compasses. The only difference is they have a sight that allows you to more easily visually align yourself with your objective. I don't like the size and weight of them though.

One thing I've always said about using a compass is that it only works if you have a map, know where you are, and know where you need to be. A lot of people say a compass will help you if you are lost. I disagree. You can generally determine cardinal directions by using the sun or stars. That's all a compass does for you. If you don't know where you are at or where you need to be to find rescue, the compass provides you little value other than helping you travel in a straight line.